1. Field of the Invention
The present invention relates to a transmission capable of setting a plurality of gear ratios selectively.
2. Related Art
As a transmission for a vehicle, there is known either an automatic transmission for switching the applied/released states of engagement devices such as clutches or brakes by judging the gear ratio on the basis of the running state of the vehicle so that the gear ratio may be achieved, or a manual transmission for setting a predetermined gear stage by selecting a plurality of gear pairs always meshing with each other on the basis of a manual operation to connect the selected gear pairs to an input shaft or an output shaft. According to the most general structure of the former automatic transmission, a gear mechanism is constructed of a plurality of sets of planetary gear mechanisms so that the power transmission line of the gear mechanism may be changed to execute a gear change by applying an oil pressure to a predetermined engagement device to bring it into engagement and by discharging the oil pressure from another engagement device to release it. According to a general structure of the latter manual transmission, on the other hand, the gear pair to participate in the torque transmission is selected by applying/releasing a synchronous coupling mechanism (or a synchronizer) with a shift fork associated with a shift lever. In the prior art, there is known the so-called xe2x80x9csemiautomaticxe2x80x9d transmission for executing the gear change by activating an actuator capable of controlling the synchronizer in the manual transmission electrically.
In the automatic transmission of the prior art thus far described, the engagement devices such as clutches or brakes to be hydraulically applied take direct participation in the torque transmission, so that they have to be reliably applied for keeping a predetermined gear ratio. For keeping the gear ratio, therefore, it is necessary to establish an oil pressure necessary and sufficient at all times for keeping the engagement devices in the applied states. Therefore, the pump power for establishing the oil pressure is a power loss of the vehicle as a whole and is a cause for deteriorating the fuel economy.
In either the manual transmission in which the gear pairs to participate in the torque transmission are selected by the manual operation or the semiautomatic transmission in which the selections are carried out by actuators, on the contrary, no manipulation force is required after the synchronizer was switched, to eliminate the disadvantage of the power loss in the above-mentioned automatic transmission. In the transmission of this kind, however, the gear change has to be executed with the input of the power to the transmission being interrupted. Therefore, the interruption of the power and the later input of the power are consecutively caused at each gear change. As a result, shift shocks may appear to deteriorate the riding comfort and the drivability.
A main object of the invention is to provide a transmission which has no power interruption at a gear change but requires no power for keeping a gear ratio.
The invention is characterized by making a construction in which such one of a plurality of transmission mechanisms interposed between a first shaft and a second shaft and having different gear ratios as participates in the transmission of a torque is selected by actuating a two-way clutch. According to the invention, more specifically, there is provided a transmission comprising: a first shaft, to which a power is transmitted from a prime mover; a second shaft for outputting the power to drive wheels; and a plurality of transmission mechanisms of different gear ratios for transmitting the power between said first shaft and said second shaft. Moreover, the transmission according to the invention is characterized: in that a two-way clutch capable of switching a torque transmitting direction into a forward direction and a backward direction is interposed between at least any of said transmission mechanisms and said first shaft or said second shaft; and in that select means is provided for selecting the torque transmitting direction of said two-way clutch.
In the invention, therefore, the two-way clutch for a predetermined transmission mechanism is set in a state to transmit the torque forward. If an upshift is effected from that state, that is, if the torque is transmitted between the first shaft and the second shaft through a transmission mechanism having a small gear ratio, the two-way clutch being applied is released in response to a change in the torque to establish the gear change. Specifically, the gear change is achieved by the change in the torque so that the power is not interrupted. Moreover, the two-way clutch keeps the applied states according to the acting direction of the torque, so that no power is consumed to keep the gear ratio.
In the invention, on the other hand, there can be adopted as said two-way clutch, a two-way clutch constructed to retain a transmission member, which is arranged between an inner ring and an outer ring for intermediating the torque transmission between said inner ring and said outer ring, by a retainer, and to turn said retainer relative to said inner ring or said outer ring thereby to switch the torque transmitting direction, and said select mechanism can include a change-over mechanism for moving axially to turn said retainer relative to said inner ring or said outer ring.
With this construction, therefore, said change-over mechanism moves forward or backward to turn the retainer by a predetermined angle. As a result, the torque transmitting direction in the two-way clutch is changed to achieve the gear change. This movement in the axial directions is similar to that for switching the synchronizer in the manual transmission or semiautomatic transmission of the prior art, so that the mechanism of the prior art for switching the synchronizer can be converted as the mechanism for operating the gear change. As a result, it is possible to lower the cost for manufacturing the transmission.
In the invention, moreover, said change-over mechanism can include: a movable member for moving said retainer to a position for transmitting the torque forward and a position for transmitting the torque backward; and a detent mechanism for retaining said movable member selectively in a first position to retain said retainer in said position for transmitting the torque forward and in a second position to retain said retainer in said position for transmitting the torque backward.
According to this construction, therefore, the retainer in the two-way clutch transmitting the torque, turns together with the inner ring and the outer ring, but the member for applying a manipulation force in the axial directions for turning the retainer with respect to the inner ring or the outer ring is stopped in the turning direction. As a result, relative rotations occur between the two-way clutch and that member. However, the movable member coupled to the retainer is retained in the first position and in the second position by the detent mechanism. Accordingly, the retainer is retained in the position for transmitting the torque forward and in the position for transmitting the torque backward. As a result, no manipulation force need not be continuously applied after the retainer was set in either position, so that the frictional contact between the movable member and the member for moving the former axially can be avoided.
In the invention, moreover, the transmission can further comprise: a selective coupling mechanism for coupling/decoupling said two-way clutch and said transmission mechanisms selectively.
With this construction, therefore, a predetermined two-way clutch is selectively coupled to the transmission mechanisms through the selective coupling mechanism so that it participates in the torque transmission through the transmission mechanisms. Therefore, one two-way clutch can be shared among the transmission mechanisms so that the number of required two-way clutches can be reduced with respect to the number of transmission mechanisms, i.e., the number of gear ratios to be set.
In the invention, still moreover, said change-over mechanism can include a member made movable in the axial directions for moving said retainer to the position for transmitting the torque forward and the position for transmitting the torque backward, and said movable member can have a retaining face on which the load to be received from said retainer is in parallel with the tangential direction of said retainer when said retainer is retained in any of said positions.
In the invention, therefore, as the movable member moves back and forth in the axial directions, the retainer turns by a predetermined angle with respect to the inner ring or the outer ring thereby to change the torque transmitting direction by the two-way clutch. In the retainer set to have the torque transmitting direction in the predetermined direction, a load is established in the direction to turn the retainer relative to the inner ring or the outer ring and is transmitted to the movable member. However, the retaining face of the movable member for receiving the load from the retainer is a face opposed to the direction parallel to the tangential direction of the retainer, i.e., a face along the directions in parallel with the axial directions. Therefore, the load to move the movable member axially is not established. Without any continuous application of the manipulation force to the movable member, more specifically, the retainer can be retained in a predetermined position of the torque transmitting direction.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.